strang



Oct. 18 1927.

J. M. STRANG PERISCOPE, TELESCOPE, AND E IKE OBSERVATIONAL INSTRUMENT 5 Sheets-Sheet 1 Filed Oct. 29, 1924 FIGZB.

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Filed Oct. 29, 1924 5 Sheets-Sheet 2 f mz 411% Oct. 18 '1927. v

' l J. M. STRANG PERISCOPE, TELESCOPE, AND LIKE OBSERVATIONAL INSTRUMENT Fi led Oct. 29, 1924 5 Sheeis-Sheet 3 W. W admit;

Oct. 18 11927.

1,615880 J. M. STRANG PERISCOPE, TELESCOPE, AND LIKE OBSERVATIONAL INSTRUMENT Filed 001;. 29, 19 24 5 Sheets-Sheet 4 FIGZ9.

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Oct. 18,1927. 1,645,880

J. M. STRANG PERISCOPE, TELESCOPE, AND LIKE OBS ERVATIONAL INSTRUMENT Filed Oct. 29, 1924 5 Sheets-Sheet 5 Patented Oct. 18, 1927.

UNITED STATES PATENT OFFICE.

JOHN MARTIN savanna, or GLASGOW, SCOTLAND, ASSIGNOR 'ro BARR AND s'rnoun LIMITED, OF GLASGOW, SCOTLAND.

IERISCOPE, TELESCOPE, AND LIKE OBSERVATION'AL INSTRUMENT.

Application filed October 29, 1924, Serial No. 746,556, and in Great Britain November 6, 1923.

able, rotationally or angularly, about the axis of the periscope for producing relative displacement ofthe two images for the measurement of angles. For an exampleof this type of periscope see specification of United States Patent No. 1,529,225.

In periscopes of the single entry beam type as previously known the system of prism for dividing the beam has been located.

in a region where rays of the beam are parallel, and as the conditions appertaining to a beam of parallel raysdiffer from those appertaining to a beam the rays of which are not parallel, say convergent, a system of prisms which is suitable for a parallel beam is not suitable for a convergent beam, principally because focus of the images is not affected when a parallel beam is being dealt with, whereas focus of the images would be affected if the same system of prism was used in a convergent beam.

The principal object of the present invention is to provide prism systems for use in periscopes of the single entry beam type suitable for location within a periscope at or in a region where rays. of the beam of light are convergent (positively convergent passing to a focal point or negatively convergent (divergent) passing from a 'focal point), the system of prisms being formed tion will now be describe or prisms of the system, or an image capable of being moved by deviation. Further, a system of prisms may be provided capable of producing a zero indication in which the principal and complementary images coincide.

By this invention, amongst other advantages, small prisms can be used, due to the fact that a portion of the convergent beam may generally be chosen where the cross-sectional area is small. With the space ordinarily available provision may be made for switching the prisms out of the beam when not required for use, thus saving the loss of light which otherwise would occur. Considerable latitude in choosing the most suitable place for the system of prisms is obtained as it may be located at any place where a convergent part of the beam occurs. For example, a system of prisms may be placed comparatively near to the eyepiece end of the periscope. The length of the actuatin rods is thus small.

For measurement 0 angles prisms of a prism system are moved relatively, rotationally or angularly, so as to impart to the images relative movement in one transverse transverse direction, for example, .by rotation bodily together or by alterin the axis about which rotation is perform Some examples of systems of prisms and their application accordin to this invenwith reference to the accompanying drawings, in which t Figure 1 is a diagram illustrating in longitudinal axial section a first system of prisms, and Figure 2 is a similar diagram illustrating modified conditions and introduced for purposes of explanation.

Figure 3 is a diagram illustrating in longitudinal axial section a second system of prisms.

Figure 4 is a diagram illustrating .in longitudinal axial section a third system-of prisms.

' Figure 5: is a diagram illustrating in longitudinal axial section a fourth system of prisms.

Figure 6 is a diagram illustrating in longitudinal axial section a fifth system .of

prisms.

igure 8 is a diagram illustrating in longitudinal axial section a seventh system of prisms.

Figure 9 is a diagram illustratingoptical parts of a periscope provided with a system of the prisms.

Figure 10 is a diagram illustrating optical parts of a periscope to be referred to.

Figure 11 is a diagram illustrating a system of the prisms-and associated mechanism.

Figure 12 is an illustration of a field showing images as may be produced with the use of a system of prisms and viewed by an observer, for'observation of angular mag-" nitude in a vertical direction.

Figure 13 is a corresponding illustration showing the images after prisms of the system have been moved by relative rotation.

Figure 14 is an illustration similar to Figure 12, for observation of angular magnitude in a horizontal direction.

In Figure 1 a system of prisms is illustrated consisting of two refracting prisms A and B of equal refracting powers placed in series in a convergent portion of the beam of a periscope. This portion of the beam as illustrated is positively convergent. Each prism is surrounded in its own plane by a second prism, F and G respectively, of comparatively small refracting power. Each central prism may be conveniently mounted on its surrounding prism and be rotated with it. The thickness of each central prism and of its surrounding prism should be substantially the same so that there be no appreciable difference of focus between the images produced by the rays passing through the central prisms A, B, and surrounding prisms F, G, respectively.

The object of making the surrounding risms F, G, with a small refracting angle is to enable the zero position to be attained. This will be understood with reference to Figures 1 and 2. In Figure 2 the prisms A and B are shown in their zero position for measurement of angles in a plane perpendicular to the paper, i. e. their maximum deviations are in the plane of the paper and are oppositely placed. It will be seen that there is a lateral shift of the axis of the beam passing through the prisms A and B, the amount of the shift depending on the inclination of the faces of these prisms to the axis, their thickness, and the thickness of the air-space between them. The image produced by light passing through the central prisms A and B is consequently shifted from C to D in the plane of the paper. If,

as shown in Figure 2, the surrounding prisms F and G are parallel pieces of glass, the complementary image will remain at C on the axis and there will, therefore, be, as shown in Figure 2 two images in the field of View and consequently no means of attaining a true zero position. If, however, the surrounding prisms F and G are made with a slight refracting angle, as shown in Figure 1, it will be seen that it is possible to deviate the image produced by them to the point D so that only one image will be seen in the field of View at the zero position.

If desired, one ofthe surrounding prisms may be made parallel and all the correcting refraction may be made on the other surrounding prism.

Instead of two surrounding (or central) prisms, we may employ only one surrounding (or central) prism, its thickness being substantially equal to the combined thickness of the two central (or surrounding) prisms.

Another alternative Way of carrying out the invention is to make one of the central prisms with a slightly greater refracting power than the other. In Figure 3 this arrangement is shown, the prism B having slightly stronger refraction than A Consequently, the axial ray which has been shifted laterally to E will not emerge parallel to the axis but may be turned back ,to form the image at C on the axis. The surrounding prisms F Gr in this case may be made parallel.

Instead of allowing at the zero position lateral shift of the beam forming the prin cipal image to take place in its passage through the system of prisms, the system may be so arranged that no such lateral shift occurs. One way of carrying this out is illustrated in Figure 4. In this case the central prisms, A and B, are placed with their outer surfaces perpendicular to the axisv of the beam and the air space between them is reduced to an extremely small quantity. If the prisms are of equal retracting power and are rotated about an axis X X, perpendicular to the inclined surface of each, there will then be no appreciable shift of the image in the zero position. This may be done by mounting each central prism in a spider like holder which can be rotated about the proper axis. In this case the surrounding prisms may be combined into one parallel prism K having its thickness substantially equal to the combined thickness of prisms A. and B and remaining stationary when the prisms A and B are rotated about the axis X X. Thus, for measurement of angles prisms A and B only require to be rotated, and to enable observations to be made in various transverse directions, the adjustment re uired in this case would involve altering t e position of the justment to be made would be by rotation of that plane about the central axis of the beam, the axis X X remaining unmoved in the plane.

Instead of causing the central prisms to produce the principal image, we may make the surrounding prisms of comparatively strong refracton and the central prisms either of .comparatively weak refraction or parallel, according to which of the above alternative methods is adopted.

Instead of using two central prisms and two surrounding prisms, it is possible to use two prisms alone covering any suitable portion of the beam. For instance, in Figure 5 prisms A and B are shown covering the central portion of the beam and'in Figure 6 prisms A and B are shown covering a portion surrounding a central portion of the beam. In order to eliminate the difference in focus between the principal image and the complementary image, a small curvature may be given to one or more of the surfaces of the prisms. This .will have the effect of magnifying the principal image produced ure 5 each prismmay conveniently be carriedby a spider-like frame.

' The method of carrying this out is indicated Instead of using the retracting prisms in series as inthe above methods, they may be arranged concentrically in the same plane.

in Figure 7. In this arrangement central rism A may be mounted in a spider-like rame and may be rotated in the opposite direction to prism B for the measurement of angles. In such a case, if the prisms are of equal refraction there will only be one image at the zero position, which is the position shown in Figure 7. Also there will be no difference in focus between the principal and complementary images. i There will be a displacement of the whole field of view, which may be a serious disadvantage if the prisms are of strong refraction. This diflioulty may be overcome by inserting a compensating stationary prism in series with the two prisms. Thus, as shown in Figure 8, a compensating prism I-I, having a'refraction substantially equal and opposite to that of either of the measuring prisms in their zero position, may be provided to cover the whole beam. With such an arrangement there will be only one image in the zero position and there will be no displacement of the field.

Figure 9 illustrates by way of example paths which the light may take in passing through the optical parts of a periscope fur nished with prisms as illustrated at Figure 5. Thus, a beam of light coming from a distant object entering the prism 2 at the head of the periscope is reflected at right angles downwards through an objective 3, collector lens at, and objectives 5 and 6. On reaching the refracting prisms system composed of the prisms A and B the beam is divided into two portions, one portion passing through the refracting prisms system,

the other passing clear of them. The beam then passes as two separate portions through the remaining optical parts of the system, namely, collector lens 7, prism 8, field lens 9, and eye lens 10. The thick edges of prisms A and B are shown as both being towards the one side of the instrument and therefore each prism deviates the light in the same direction. The result is that the portion of prisms will form a principal image of the object at E in a different position from the complementary image formed at E by the portion of the beam which does not pass through the prisms.

In this case the images seen would be as indicated in Figure 12, and in order to measure the angle subtended by, say, the distance between the top of the mast of the ship and the waterline, the. refraction requires-to .be

reduced so as to bring the top of the mast in the deviated image E to touch the waterline in the complementary image E as indicated at Figure 13, to accomplish which the prisms A and B require to be rotated in opposlte directions; The angular position of the prisms relative to their zero position then gives a measure of the angle subtended. Figure 14 indicates the position of the images when measurements of angle in the horizontal plane are to be made.

. Some other positions which prisms systems may occupy according to this invent on are indicated in Figure 10 by dotted llnes P, P P or P At positions P, P, the portions of the beam are positively convergent and at positions P P are negatlvely convergent.

In Figure 11 the prisms A "and B of a system are mounted capable of rotation in a carrier B. Each prism is provided with a older toothed about its periphery tomesh with pinions S and T, connected to rotate with helical pinions S and- T respectively.

The pinions S? and T, which are of oppomesh with a pinion 13. By operating 13 the prisms are rotated relatively in opposite di-' the beam of light-which passes through the rections and by 11 rotated bodily together. A scale 14 is provided to rotate with the pinion 13.

The carrier R is pivoted to turn about an axis at 15 being operated by connection with a rack 16 and pinion 17. A fixed segment Y is provided having a single tooth 18 to engage with teeth of the prism holders to prevent their rotation when removed from gear with the pinions S, T.

I claim 1. An angle measuring periscope of the single entry beam type having optical parts for causing rays of the beam of light to be convergent, a system of prisms within the periscope located in a region where rays of the beam of light are convergent, the system of prisms being formed to divide the beam into two portions, for producing two images, and formed to cause the two images to lie in one and the same focal plane, one a principal image, the other a complementary ima e, and for deviating the principal image aving prisms of the system relatively movably rotationally angularly about an axis extendinglongitudinally in the beam.

2. An angle measuring periscope of the single entry beam typp having optical parts for causing rays of t e beam of light to be convergent, a system of prisms within the periscope located in a region where rays of the beam of light are convergent, the system of prisms being formed to divide the beam into two portions for roducing two images,

' and formed to cause t e twoimages to, lie in one and the same focal plane, means for im parting to prisms of the system relative rotary movements for measurement of angles, and means for adjusting prisms of the system to enable observations to be made in various lateral directions.

3. An angle measuring periscope of the single entry beam type having optical parts for causing rays of the beam of light to be convergent, a system of prisms within the periscope located m a region where the beam of light is convergent, the system of prisms being formed to divide the beam into two portions, for producing two images and formed to cause the two images to lie in one and the same focal plane, one a principal image, the other a complementary image, and for deviating the principal image having prisms of the system relativethe beam of light are convergent the system of prisms being formed to divide the beam into two portions, for roducing two images, and formed to cause t e two images to lie in one and the same focal plane, the two images being one a principal image, the other a complementary image, the complementary image being an undeviated image and the principal imagesbeing capable of deviatiomfor the purposes set forth.

5. An angle measuring periscope of; the single entry beamtype having optical parts for causing rays of the beam of light to be convergent, a system of prisms within the periscope located in a region where rays of the beam of light are convergent, the

system of prisms being formed to divide the beam into two portions, for producing twoimages, and formedto'cause the two images to lie in one and the same focal plane, the

two images being one a principal ima e in 4 the production of which the prisms o the system are used, the other a complementar image produced by optical parts of the periscope, and the principal image being capable of deviation, for the purposes set' forth.

for. producing two images and formed to cause the two images to lie in one and the same focal plane and means for imparting to the prisms relatively rotary movements,

.for the purposes set forth.

7."An angle measuring periscope of the single entrybeam type having optical arts for causing rays of the beam of light to be convergent, a system consisting of two prisms placed in series within the periscope located in a region where rays of the beam of light'are convergent, the prisms covering a portionT'of the beam, the system of prisms being formedto divide the beam into two portions for producing two images and for'rned to cause the two images to he 111 one and"the same focal plane, and means for imparting to the prisms relatively rotary movements, for the purposes set forth.

8} An angle measuring periscope of the single entry beam type having optical parts for causing rays of the beam of hght to be convergent, a system consisting of two prisms within the periscope located in a region where rays of the beam of light are convergent, the prisms covering a central ortion of the beam, the system of prisms eing formed to divide the beam into two ortions for producing two images and ibrmed to cause the two images to lie in one and the same focal plane, and means single entry beam type having optical parts for causing rays of the beam of light to be. convergent, a system consistin of two prisms withinLthe periscope locate in a region where rays of the beam of light are convergent, the prisms of the system having a small curvature given to one or more'surfaces of the prisms, and means for imparting to the prisms relatively rotary move ments, for the purposes set forth.

10. An anglc measuring periscope of the single entry beam type having optical parts for causing rays of the-beam of light to be convergent, a system consisting of two prisms placed in series within the periscope located in a region where rays of the beam of light are convergent, the prisms covering a portion ofthe beam, the prisms of the system having a small curvature given to one or more surfaces of the prisms, and means for imparting to the rlsms relative- 1y rotary movements, for t e purposes set forth.

11. An angle measuring periscope having optical parts for causing rays of the beam of light to be convergent, a system of prisms 5 within the periscope located in a region where rays of the beam of light are convergent, mechanism for rotating prisms of the system in opposite directions relatively to one another and together bodil comprising two helices of opposite han and two helical pinion wheels of opposite hand, the

helices capable of rotation and endwise movement being arranged to mesh with the helical pinions 1n complementa pairs, one with each, the helical pinionsbemg adapted to rotate the prisms, for the purposes set v forth,

JOHN MARTIN STRANG. 

